Re: Request for feedback on statistical method
From: Einar Andreas Rødland (e.a.rodland_at_labmed.uio.no)
Date: 11/03/04
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Date: Wed, 03 Nov 2004 17:04:17 +0100 To: Shepherd Moon <shepherdmoon@yahoo.com>
Shepherd Moon wrote:
> There is one article that claims to have analyzed this claim
> statistically and claims that there is a "95% confidence level" that
> the speed of light has actually been decreasing over time. I'm trying
> to find out if this trend is real or artifactual. I suspect it is
> artifactual but am not a statistics expert.
Ross Clement has already made some good points. There are more, though.
As methods and technology has improved, we have been able to make more
and more accurate measurements. Thus, more recent measurements are
more accurate than the older ones. The statistical method used,
however, assumes (as far as I can see) that the estimation errors are
random and of constant magnitude, which is clearly not the case.
Errors in physical experiment may be of several kinds: they may be
statistical errors (related to random measurement errors) or they may
be systematic errors (related to the method or experiment). The random
measurement errors may be assumed to be independent from experiment to
experiment, but systematic errors can not be expected to be
independent. E.g., some of the early methods used stellar aberation
http://scienceworld.wolfram.com/physics/StellarAberration.html
which depends on knowing the speed of the Earth around the Sun; if the
estimate of this speed is too high, it would consistently give too
high estimates of c no matter how accurate the measurements are; other
methods will have similar kinds of systematic errors. Thus another
basic assumption is unfounded...or at least lacking a proper motivation.
If you take a look at the light speed estimates at different times,
the difference from the presently known value is typically in the same
order as the stated uncertainty of the estimates. This is typical of
certain 'remarkable claims': they tend to be based on deviations that
are just about the same magnitude as the uncertainties...and these
deviations tend to decrease as the methods improve. The author,
however, seems to favour the explanation that the speed of light has
changed gradually until around 1960 when it converged very quickly
towards the value know today: it seems somewhat arbitrary for a
physical constant, after 6000 years of change, to suddenly stabilize
just as we start to measure it accurately.
Another thing is that today the speed of light is constant by
definition: it is the conversion factor between metres and seconds,
where one (don't remember which) is defined in terms of the other
given the defined value for c. The only fundamental dimensionless
constant is the fine structure constant:
http://scienceworld.wolfram.com/physics/FineStructureConstant.html
If this changes, it will not be possible (or meaningful?) to tell
which of the underlying physical constants have changed.
If the fine structure constant (or speed of light) had changed
dramatically in the last 6000 years, I'd think that should have given
very clear effects on the spectra of moderately distant stars...but
probably sci.physics would be the right place to ask about that. I
recall some time ago there was a report, from serious reasearchers,
indicating that it may have changed; but they were talking about the
early hours of the big bang, not the 'creation of the universe 6000
years ago'. I'm not certain what the final verdict was; but, again,
sci.physics should be the right place to ask.
> The statisitical article is here:
>
> Is the Velocity of Light Constant in Time?
> by Alan Montgomery
> Mathematician
> 218 McCurdy Drive, Kanata, Ontario K2L 2L6 Canada
> and
> Lambert Dolphin
> Physicist
> 1103 Pomeroy Avenue, Santa Clara, CA 95051
> http://www.ldolphin.org/cdkgal.html
>
> The original article is here:
> The Atomic Constants, Light, and Time
> by BARRY SETTERFIELD
> and
> TREVOR NORMAN
> http://www.setterfield.org/report/report.html
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